What exactly is the big trade meeting in Cancún about? It is, in the jargon, a mid-term ministerial meeting of the Doha development round. Trade negotiations have taken place in "rounds" since shortly after the second World War. During each round all the participants in the international trade system - now numbering 146 countries - spend a couple of years putting together a deal which lowers barriers to international trade.
To introduce another piece of jargon, this means agreements are multilateral, in other words they involve all countries. The World Trade Organisation oversees this process. The current round started in Doha, Qatar, in November 2001 and is due to finish by the end of next year. Most negotiation is conducted by officials and the mid-term ministerial meeting is designed to give the process a political push, though not to strike a final deal.
Didn't the GATT organisation used to have something to do with this?
Yes, the GATT oversaw trade negotiations through successive rounds since 1947. Under the previous talks - the Uruguay round - the participants agreed to set up the World Trade Organisation as a fully-fledged arbiter and negotiating body on world trade. It had a dodgy start, failing to launch the current round in a fractious meeting in Seattle in 1999, before agreement on the terms of the development round in Doha.
Why the development round?
Because it is meant primarily to address the needs of developing countries that complain the world trade system is stacked against them.
And will it?
That depends. In the run-up to Cancún the developing countries were saying the rich world must lead the way in opening its markets, particularly in agriculture. However, the developed countries are under pressure from producers not to cut barriers too quickly. This will be one of the crunch points of the talks.
Surely its not all about agriculture?
Not at all. The talks cover a host of other areas. Negotiators have been haggling since the round started about measures to free up trade in manufacturing and services, the protection of intellectual property rights and whether rules on investment and environmental protection are properly dealt with by the WTO process. The detail is mind-boggling complex and the round generally operates on the basis that "nothing is agreed until everything is agreed".
What if the talks fail?
Nobody knows, though that won't stop them issuing dire warnings about the consequences of failure. The multilateral negotiation process has been under way for so long that it is not clear what happens if it fails. However, it would certainly damage economic confidence and would threaten a slide to bilateral trade deals and possibly even new tariff barriers - import taxes which countries use to protect their markets.
And the protesters?
These fall broadly into two - sometimes overlapping - groups. There are the anti-globalisation groups who oppose the idea of free markets and free trade and those interested in development issues, who argue that huge change is needed to give developing countries a fair break.
